1. Field of the Invention
The present invention relates to a material, and a process for producing same, which is suitable for use in fabricating components of the valve-actuating mechanism of an internal combustion engine. More particularly, the invention relates to a material suitable for fabricating members subjected to very frequent slide-contact with a cam member, i.e., for members such as rocker arms and valve lifters which make up the valve-actuating mechanism of an internal combustion engine.
2. Description of Relevant Art
Valve-actuating mechanism components of internal combustion engines, particularly members such as rocker arms and valve lifters which are repeatedly subjected to very frequent slide-contact with a cam, require for their fabrication a material having special properties.
With reference to the accompanying drawings, the general structure of valve-actuating mechanisms of internal combustion engines will be described.
An example of an OHC-type valve-actuating mechanism of an internal combustion engine is shown in FIG. 1. In response to rotation of a cam 2, a rocker arm 1 undergoes a seesaw motion, and thereby the rocker arm 1 alternatingly opens and closes a valve 5. In a valve-actuating mechanism of this type, the abrasion resistance of the working face of the rocker arm 1, which working face is brought into frequent slide-contact with the cam 2, becomes the most critically important feature.
With reference to FIG. 2, there is shown an example of a valve-actuating mechanism of the push rod type. A valve lifter 3 and push rod 4 are interposed between the cam 2 and rocker arm 1, thereby transmitting the motion of the cam 2 to the valve 5. In a valve-actuating mechanism of such type, the most critical feature resides in the abrasion resistance of the working face of the valve lifter 3, which working face is brought into frequent slide-contact with the cam 2.
In each of the above-described types of valve-actuating mechanisms, it is of course important that the aforesaid working faces have superior abrasion resistance as mentioned above. In addition, it is also important that the working face does not wear or abrade the cam 2, which is the member operatively cooperating with the working face.
The aforesaid members have heretofore been fabricated generally of an iron-base material such as a steel or alloyed cast iron. In order to enhance their abrasion resistance, prior to their use, the working faces cooperating with the cam 2 have been subjected to a treatment such as surface hardening through heat treatment, chilling, hard chromium plating or flame spraying of an autogeneous alloy.
However, such treated prior art materials have attendant problems, such as that carburized steel is poor in durability, and a hard chromium plated material is likely to be subject to chipping-off due to localized contacts or abrasion. On the other hand, where an autogeneous alloy is flame-sprayed, there arises another disadvantage with regard to fabrication cost due to increased fabrication steps and use of expensive raw materials as well as uncertainty in providing quality assurance, due to the inclusion of the flame-spraying step.
In view of the foregoing problems, there has developed a desideratum for superior materials for use in fabricating components of valve-actuating mechanisms of internal combustion engines. The present invention eminently fulfills such desideratum, and effectively overcomes the foregoing problems attendant prior art materials used in fabricating components of valve-actuating mechanisms of internal combustion engines.